1. Field of the Art
The present invention is directed to a heart valve holder and more particularly to a device for holding a stentless tissue heart valve prosthesis during implantation and to a combination stentless tissue heart valve prosthesis and detachable holder.
2. Discussion of the Prior Art
Surgically-implanted heart valve prostheses have extended the life expectancy of many patients who had defective natural valves. Such prostheses can be either mechanical or derived from human or animal donors. The aortic prosthesis is implanted in the patient during a surgical procedure in which a segment of the aorta nearby the natural valve is slit open so that the malfunctioning leaflets can be cut out and the prosthetic valve is sutured within an intact segment of the aorta adjacent to the heart. The surgical procedure is exacting due to the surgeon's cramped quarters. Holding the implant in place while the surgeon places the sutures to attach it to the interior of the patient's aorta presents an especially difficult problem.
To aid the surgeon during the implant procedure, it is known to use both disposable and nondisposable holders to position the valve during surgery. However, the known valve holders are large and cumbersome. For instance U.S. Pat. No. 3,409,013 describes a nondisposable surgical instrument having a shank with pivotal bowed jaws mounted at one end for gripping a heart prosthesis having a suture ring by the suture ring. Means is also provided for holding taut a plurality of sutures to be passed through the suture ring attached to the valve. The sutures are meant to be used in securing the prosthetic valve into the patient's aorta. A more recent development is the disposable valve holder disclosed in U.S. Pat. No. 4,185,636, which also utilizes a plurality of circumferentially spaced legs attached to central holder apparatus. The sewing ring of the prosthetic heart valve is attached by sutures to a holding disc slideably positioned upon the central rod of the valve holder. These known valve holders, however, are unwieldy and obstruct the surgeon's view. Moreover, this type of valve holder requires that the prosthetic valve have a sewing ring for grasping by the holder or to which the holder is laboriously attached by sutures immediately prior to the surgery.
Each of the known types of prosthetic heart valve also has its peculiar limitations. For instance, homografts from donor human hearts are difficult to obtain in exact sizes, cannot be sterilized, and require extensive tests to determine the risks of transmitting diseases and of donor tissue incompatibility. Mechanical implants, although readily available in many types and sizes, do not duplicate the natural means of attaching the leaflets to the aortic wall and are excessively rigid, thus making installation difficult.
Bioprostheses procured from animals provide an acceptable alternative to homografts and mechanical valves because they can be provided in acceptable quantities and in a variety of sizes, they are more flexible than mechanical models, and they can be sterilized and tested for disease. However animal valves are commonly trimmed by cutting away the aortic wall between the leaflets and leaving only the tissue to which leaflets are attached. To support the remaining structure, animal valves are usually supported by metallic or plastic stents, often augmented by a sewing ring usually attached to the exterior of the prosthesis to aid in surgical attachment into the patient's aorta. The sewing ring and/or stent occupies space in the patient's annulus, thereby reducing the orifice area of the valve and consequently increasing turbulence and the pressure gradient. In addition, the stent tends to be somewhat rigid, requiring the leaflets to absorb much of the stress during valve closure. Because the heart beats approximately 40 million times per year with closing pressures up to 4 psi, significant fatigue and wear can occur to a heart valve leaflet when it must absorb the stress caused by heartbeat.
It is common practice to tan animal valves to render the animal tissue relatively inert with respect to the living host environment and to provide a fixed configuration. As disclosed in Hancock et al U.S. Pat. Nos. 3,966,401 and 4,050,893 and Angell et al U.S. Pat. No. 3,983,581, animal heart valves can be tanned using a tanning fluid under differential pressures across the valve ranging from 20 mm Hg to 120 mm Hg. However, it is known that obtaining fixation at these high internal pressures results in considerable loss of resilience to the collagen fibers in the heart valve. As disclosed in Lane U.S. Pat. No. 4,372,743, a preferred method of fixation at low pressure eliminates these difficulties. According to this low pressure method, fixation of an animal heart valve is accomplished without substantial loss in resilience to the internal collagen fibers and without shrinkage of the valve by subjecting it to a tanning fluid, preferably glutaraldehyde, at a differential pressure across the valve of from zero to 4 mm Hg. In this procedure, an internal mechanical restraint is positioned within the valve prior to fixation so as to prevent shrinkage and distortion of the valve during the fixation step. The internal restraint is removed once the valve has been tanned.
Despite the advantages provided by low pressure tanning, it can be seen from the foregoing discussion that the need exists for new and improved aortic heart valves, especially those derived from animal donors, and for holders that aid in their surgical implant.